The invention relates to cooling in a gas turbine and, more particularly, to a double wall bearing cone that closes the opening between the bearing housing and the exhaust frame structure in a gas turbine.
A bearing cone is a barrier wall in a gas turbine that closes the opening between the bearing housing and the exhaust frame structure of the gas turbine. As shown in FIG. 1, this barrier wall 100 creates a cavity 102 around the rotor aft shaft 104 and the turbine third stage wheel 106 that is supplied with purge air to prevent leakage of hot turbine exhaust gas into the cavity 102. Normally, air discharging from the exhaust frame cooling circuit is used to pressurize and purge the rotor aft shaft cavity 102.
Problems resulting from wear have been noted in the turbine third stage wheel and rotor aft shaft rabbet joint due to adverse thermal gradients in the rotor created by the purge air conditions in the aft shaft cavity. Impingement of exhaust frame cooling air on the aft face of the third stage wheel and leakage of cold bearing tunnel air across the bearing cone into the rotor aft shaft cavity (see arrows in FIG. 1) are major contributors to the adverse thermal gradients.